<Electric Vehicles and Hybrid Vehicles>
In electric vehicles and hybrid vehicles, an inverter is used for converting a DC voltage of a battery to an AC voltage, and variable speed control is performed on a motor by means of an AC output from the inverter.
A pulse-width modulation (PWM) type inverter is used as the inverter. In the pulse-width modulation (PMW) type inverter, a sine-wave command is generated as a voltage command, and the value of a triangular wave carrier is compared with the value of the sine-wave command. Based on a pulse signal thus obtained, a gate signal is generated to operate a switching device. However, the AC voltage output from the inverter does not have a perfect sinusoidal waveform but has a shape in which rectangular waves with different widths are piled up continuously. Therefore, in a corner part of each rectangular wave where a voltage change rate changes suddenly, a surge voltage may be generated due to resonance, reflection or the like in a line between the inverter and the motor.
There are two typical methods for addressing a surge voltage in the background art, that is, (1) a method using a filter (see Patent Documents 1 to 3) and (2) an electromagnetic shielding method.